Study associates vitamin D deficiency with childhood infections

THE vitamin D levels of newborn babies
appear to predict their risk of respiratory
infections during infancy and the
occurrence of wheezing during early
childhood, but not the risk of developing
asthma. Results of a study in the January
2011 issue of Pediatrics support the theory
that widespread vitamin D deficiency
contributes to risk of infections.
“Our data suggest that the association
between vitamin D and wheezing, which
can be a symptom of many respiratory
diseases and not just asthma, is largely due
to respiratory infections, ” says Dr. Carlos
Camargo, of the Massachusetts General
Hospital (MGH), who led the study. “Acute
respiratory infections are a major health
problem in children. For example,
bronchiolitis - a viral illness that affects
small airway passages in the lungs - is the
leading cause of hospitalisation in U.S.
infants. ”
Although vitamin D is commonly associated
with its role in developing and maintaining
strong bones, recent evidence suggests that
it is also critical to the immune system.
Vitamin D is produced by the body in
response to sunlight, and achieving
adequate levels in winter can be
challenging, especially in regions with
significant seasonal variation in sunlight.
Previous studies by Camargo ’s team found
that children of women who took vitamin D
supplements during pregnancy were less
likely to develop wheezing during
childhood.
The current study was designed to examine
the relationship between the actual blood
levels of vitamin D of newborns and the risk
of respiratory infection, wheezing and
asthma.
The researchers analyzed data from the
New Zealand Asthma and Allergy Cohort
Study, which followed more than 1,000
children in the cities of Wellington and
Christchurch. Midwives or study nurses
gathered a range of measures, including
samples of umbilical cord blood, from
newborns whose mothers enrolled them in
the study. The mothers subsequently
answered questionnaires - which among
other items asked about respiratory and
other infectious diseases, the incidence of
wheezing, and any diagnosis of asthma -
three and 15 months later and then
annually until the children were five years
old. The cord blood samples were analysed
for levels of 25-hydroxyvitamin D (25OHD) -
considered to be the best measure of
vitamin D status.
Cord blood samples were available from
922 newborns in the study cohort, and
more than 20 percent of them had 25OHD
levels less than 25 nmol/L, which is
considered very low. The average level of
44 nmol/L would still be considered
deficient - some believe that the target level
for most individuals should be as high as
100 nmol/L - and lower levels were more
common among children born in winter, of
lower socioeconomic status and with
familial histories of asthma and smoking. By
the age of 3 month, infants with 25OHD
levels below 25 nmol/L were twice as like to
have developed respiratory infections as
those with levels of 75 nmol/L or higher.
Survey results covering the first five years
of the participants ’ lives showed that, the
lower the neonatal 25OHD level, the higher
the cumulative risk of wheezing during that
period. But no significant association was
seen between 25OHD levels and a physician
diagnosis of asthma at age 5 years. Some
previous studies had suggested that
particularly high levels of vitamin D might
increase the risk for allergies, but no such
association was seen among study
participants with the highest 25OHD levels.
Camargo notes that very few children in
this study took supplements; their vitamin D
status was determined primarily by
exposure to sunlight.
An associate professor of Medicine at
Harvard Medical School, Camargo notes that
the study results do not mean that vitamin
D levels are unimportant for people with
asthma. “There’s a likely difference here
between what causes asthma and what
causes existing asthma to get worse. Since
respiratory infections are the most common
cause of asthma exacerbations, vitamin D
supplements may help to prevent those
events, particularly during the fall and
winter when vitamin D levels decline and
exacerbations are more common.
That idea needs to be tested in a
randomized clinical trial, which we hope to
do next year. ”